This invention relates generally to the production of ice and relates, more particularly, to the production of ice from a medium, such as carbon dioxide, which is gaseous when at room temperature and atmospheric pressure.
Ice, such as dry ice, is commonly used for the refrigeration of food products, for shipping of chilled packages and for use, when combined with compressed air or turbine wheel accelerators, as a blast media for cleaning surfaces.
Prior art processes used to form dry ice pellets of relatively high density commonly involve the flashing of liquid carbon dioxide into solid carbon dioxide snow which is subsequently compacted and formed into pellets via presses, by ram extrusion or by rotary extrusion. The density of the formed pellets formed by these processes is largely dependent upon parameters attending the extrusion step and can approach, but rarely achieves, the maximum density of solid carbon dioxide. Furthermore, the size of the pellets formed in such processes is normally determined by the sizes of the openings provided in plates associated with the extrusion step.
A limitation associated with prior art pellet-forming processes, such as the flashing/pressing technique described above, relates to the fact that only about forty percent of the liquid carbon dioxide is converted to solid while about sixty percent is converted into gas. Consequently, methods have been employed to convert a higher percentage of the liquid carbon dioxide into solid during pellet-forming processes. For example, one method described in U.S. Pat. No. 5,257,503 reclaims the lost carbon dioxide by capturing, compressing and re-liquefying the flash gas. Another method, addressed in each of U.S. Pat. Nos. 1,863,377, 2,138,758 and 3,901,044 involves a refrigeration unit which cools and directly freezes liquid carbon dioxide into solid form in molds, thereby eliminating the flashing step. The freezing of liquid in molds, however, requires the use of relatively complicated mechanisms to release the pellets from the molds. It would be desirable to provide a method and system for producing dry ice pellets in a manner which circumvents any need for or use of liquid carbon dioxide.
Accordingly, it is an object of the present invention to provide a new and improved process and system for producing ice from a process medium which is normally gaseous at room temperature and atmospheric pressure, such as gaseous carbon dioxide.
Another object of the present invention is to provide such a process and system which is capable of converting a relatively high percentage of available gas, such as gaseous carbon dioxide, into solid form, i.e. ice, wherein the solid form possesses a very high density.
Still another object of the present invention is to provide such a process and system which circumvents the need or use of a process medium when in a liquid phase.
Yet another object of the present invention is to provide such a process and system which requires no moving parts which must directly contact the ice forms, such as pellets, during production.
A further object of the present invention is to provide such a method or system which is well-suited for use in a process requiring gas pumping or in some other vacuum pump application.
A still further object of the present invention is to provide such a process and system which is capable of making ice and/or ice pellets of a predetermined shape and size.